Stain prevention in color photography



Patented Aug. 22 1944 STAIN PREVENTION IN COLOR PHOTOGRAPHY ArnoldWeissberger and Paul W. Vittum, Rochester, N. Y., assignors to Eastman Kodak-Company, Rochester, N. Y., a.

Jersey corporation of New No Drawing. Application April 15, 1943, SerialNo. 483,186

11 Claims. (Cl. 95'-6) This invention relates to color photography and particularly to a method for preventing the formation of color fog or stain in photographic emulsions.

The method of color photography in which color-forming or coupler compounds combine with the development product of aromatic amino photographic developers to produce dyes is well knovm. The color formers or couplers may be added directly to the emulsion layers or may be incorporated in the developing solution as described in Fischer U. S. Patent 1,102,028, granted June 30, 1914, or they may be incorporated in a water-permeable medium which is insoluble in the carrier for the sensitive silver salt as described in Mannes & Godowsky U. S. Patent 2,304,940, December 15, 1942, and Jelley and Vittum U. S. Patent 2,322,027 granted June 15, 1943.

A difiiculty frequently encountered in these processes is the formationof color fog or stain. When the exposed material is developed in a color forming developer, 'dye fog is frequently formed in the emulsion layer. This is because the developing agent has been oxidized to some extent by the action of the air and the oxidized developer tends to couple with the color-forming compound at places in the photographic material where no silver image is produced. It is well known that in these processes the dye should be formed only where the silver halide is reduced to metallic silver, thereby oxidizing the developing agent to a form which couples with the color former. Once the developing agent is oxidized, it couples immediately with the color former whether a photographic image is present or not. Aerial oxidation of the developer or oxidation by means other than the photographic image therefore converts thedeveloper to a form which will immediately react with the color former to produce a color fog or stain, This efiect is especially noticeable in materials having couplers incorporated in the sensitive emulsion layer since there is no coupler in the developing solution to react with any developingagent which is oxidized by the action of the air. Fog or stain arising from these causes is not readily controlled by the same procedures used to control silver fog.

One method for controlling color fog or'stain has been described inVittum and Wilder U. S. patent application Serial No. 404,894, filed July 31, 1941. One disadvantage of the method of that application is that some of the compounds, when incorporated in an emulsion containing a coupler, tend to render the resulting dye unstable to the action of light. While the color fog or stain produced on development is eliminated,

- the resulting dye is in some cases less stable than tion to provide a novel means for reducing or eliminating the formation of color fog in photographic emulsions. A further object is to provide a color-forming photographic emulsion having non-diffusing couplers incorporated therein which is not subject to the formation of color fog, A further object is to provide stain inhibitors for incorporation in photographic emulsion layers containing couplers which do not impair the stability of the dyes produced in the emulsionlayer. Otherobjects will appear from the following description of our invention. I

These objects are accomplished by subjecting an exposed photographic emulsion to a colorforming development in the presence of dihydroxy maleic acid or an ester or amine salt of I dihydroxy maleic acid.

it would be without the stain inhibitor in the emulsion.

It is, therefore, an object of the present inven- We have found that color fog or stain in in.- corporated coupler materials may be appreciably reduced by adding to the emulsion layers before coating or after coating and before processing a non-diffusing ester or amine salt of dihydroxy maleic acid. It is believed that these substances exert an anti-oxidant action either by preventing the formation of extraneous oxidized developer or by reducing any extraneous oxidized developer before it has an opportunity to react with a color former; Whatever the mechanism of the reaction, we have found it possible to reduce markedly the fog or stain density without seriously reducing the densities of the developed dye images.

The agents used according to our invention may be incorporated in single layer coatings or in one or more layers of a multi-layer coating. It may be desirable, or example, to have the stain inhibitorv present in only one or two layers of a multi-layer coating and in this case a substance would be used which does not wander frequently in gelatin. In cases where the reducing agent was desired to be uniformly distributed throughout the whole film, one might use compounds of lower molecular weight which diffuse to some extent throughout the film. When the inhibitor is intended to be nondifiusing in the gelatin, we preferably use a dihydroxy maleic acid ester of an aliphatic alcohol containing at least five carbon atoms.

When the stain inhibitor is used with emul sions containing a coupler dissolved in waterpermeable,water-insoluble agents such as those described in Mannes and Godowsky U. S. Patent 2,304,940 and Jelley and Vittum, U. S. Patent 2,322,027, it may be added either to the emulsion itself or to the coupler-carrier along with the coupler,

The stain inhibitors of our invention may also be incorporated in non-sensitive layers of the photographic material such as filter layers, inter-layer. and overcoating layers.

Where the stain inhibitor is introduced after coating and before processingnthe photographic material should be bathed in a solution of the inhibitor just prior to the color development step.

.The inhibitor may be incorporated in a pre-bath velopment solution itself The following compounds are suitable for use according to our invention:

prior to the color development step or in the de- 'pler incorporated therein and, as an inhibitor of color fog, a dihydroxy maleic acid ester of an aliphatic alcohol containing at least five carbon atoms. A

2. A color-forming photographic silver halide emulsion, comprising a non-diffusing color coupler incorporated therein and, as an inhibitor of ,color fog, di-n-amyl-dihydroxy maleate.

3. A color-forming photographic silver halide emulsion comprising a non-diffusing color coupler incorporated therein and, as an inhibitor of I color fog, dilauryl-di-hydroxymaleate.

4. The method of preventing the formation of color fo in a photographic silver halide emulsion which is developed by a color-forming development step comprising subjecting said emul- The first three compounds arerelatively soluble in water and may be used to reduce stain by incorporating them in a prebath or in a color developing solution. The latter three compounds nitrate solution of Example 1 of Mannes' and Godowsky U. S. Patent 2,304,940 and the emul-' sion prepared in the manner describedin that example. I

The following formula is suitable for a prebath of the stain inhibitor to be used prior to the color-forming development step if the 'inhibitor is not incorporated in the sensitive ma-' terial: I

Dihydroxymaleic acid gram 0.5

Sodium gulf-Ito dd 2.0 Potassium bromide ..L e do 5.0 Water to v I ately before the colordevelopment step.

Our. process is particularly useful with paper materials where it is especially important-to reduce the minimum or fog densities. This applies both to negative developing paper and to reversal paper aswell as transparency materials.

It will be understood that the, examples and modifications disclosed herein are by way off The colored photographic materiai is treated for one or two minutes in the prebath immedision to the color-forming development in the presence of'a dihydroxy maleio acid selected from the class consisting of the freeacid and the esters and amine salts of said acid. k

5. The method of preventing the formation of color fog in a photographic silver halide emulsion which is developed by a color-forming 'de-f velopment step comprising subjecting said emulsion to the color-forming development in the presence of an ester of di-hydroxy maleic acid.

6. The method of preventing the formation of color fog in a photographic silver halide emulsion which is developed by a color-forming de velopment step comprising subjecting said emulsion to the color-forming development in the presence of an amine salt of dihydroxy maleic acid.

'7. The method of preventing the formation of color fo in a-photographic silver halide emulsion which is developed by a color-forming de- 'velopm'ent step comprising subjecting said emulsion to the color-forming development in the presence of dihydroxy maleic-acid.

8. The method of preventingthe formation 0 color fog in; a gelatino-silver halide emulsion which contains a non-diffusing color coupler comprising incorporating in said emulsion as an inhibitor of color fog it-dihydroxy maleic acid ester of an aliphatic-alcohol containing at least .five carbon atoms.

inhibitor of color fog di-n-a nyli-di-hydroxy maleate.

'10. The method of preventing the formation 5 of color fOg in a photographic silver halide emulsion which contains a non-diffusing color coupler comprising bathing said emulsionafter coatin'g and just prior to a color-forming develop.- ment step in a solution of a dihydroxy maleic :acid selected from the class consisting of thefree acid and its soluble esters.

' ii. The method of preventing the formation of color fog in a photogr phic silver halide emulsion which contains anon-diffusing color coupler comprising bathing said emulsion after coating' and just prior to a color. forming, development stepin a solution-oi" dihydroxymaleic acid example only and that our invention is tobetaken mom wmssnmana. PAUL-mm 

